On Thu, Mar 12, 2020 at 09:19:39AM +0000, David Howells wrote: > Hi Matthew, > > Is ext4_dio_read_iter() broken? It calls: > > file_accessed(iocb->ki_filp); > > at the end of the function - but surely iocb should be expected to have been > freed when iocb->ki_complete() was called? > > In my cachefiles rewrite, I'm seeing the attached kasan dump. The offending > RIP, ext4_file_read_iter+0x12b is at the above line, where it is trying to > read iocb->ki_filp. > > Here's an excerpt of the relevant bits from my code: > > static void cachefiles_read_complete(struct kiocb *iocb, long ret, long ret2) > { > struct cachefiles_kiocb *ki = > container_of(iocb, struct cachefiles_kiocb, iocb); > struct fscache_io_request *req = ki->req; > ... > fput(ki->iocb.ki_filp); > kfree(ki); > fscache_end_io_operation(req->cookie); > ... > } I'm not exactly sure what you're rewriting, although from this excerpt the way that this is implemented would sure cause the UAF in ext4_dio_read_iter(). I don't forsee any issues with calling file_accessed(iocb->ki_filp); prior to calling into the iomap infrastructure, unless I'm totally missing something obvious... /M